1. Field of the Invention
This invention relates to stator assemblies for gas turbine engines and particularly to assemblies having ceramic vanes.
2. Description of the Prior Art
Scientists and engineers practicing within the turbine engine field have long recognized that ceramic materials are generally more compatible with the high temperature fluids of gas turbine engines than are conventional metallic materials. They have also recognized that the stator vanes of the turbine section are among the most susceptible of engine components to thermal and chemical degradation. It is, therefore, that a continuing search has been underway for structures which effectively integrate ceramic material and gas turbine technologies to provide turbines having increased durability.
Collaterally, increasing emphasis on the effective use of energy resources is making performance demands on turbine machinery which do not appear to be within the capacity of conventional metallic structures to obtain. Sharply elevated turbine inlet temperatures are requiring cooling systems of increasing capacity and complexity. Such systems siphon substantial working medium fluids from the flow path of the machine. The siphoned fluids are unavailable for work upon the reaction surfaces of the machine and lower engine performance results.
Prior to the concepts described herein, no commercially suitable combination of ceramic material and turbine technologies has been advanced. Of the concepts proposed, however, U.S. Pat. No. 3,867,056 to Schaller et al entitled "Ceramic Insulator for a Gas Turbine Blade Structure" is representative of numerous ceramic techniques which were heretofore known within the art. In particular, note should be taken of FIG. 1 of Schaller wherein the ceramic blades extend radially between an inner metallic shroud 22 and an outer metallic shroud 26 to form a stator assembly. The ceramic blades replace more conventional metallic blades to improve the thermal compatibility of the stator assembly with the hot gas of the flow path extending therethrough. Schaller et al. further teaches that the shroud and vane assemblies be segmented. (See column 1, line 62 and column 2, line 2.) In this respect, the typical prior art structure, as represented by Schaller, is conceptually and structurally distinct from the concepts of the present invention which are discussed in detail later in this disclosure.
Certain ceramic material concepts previously known within the art are also beneficially employed within the structure of the present invention. Specifically, ceramic materials are known to have their greatest strength under compressive, as distinguished from tensile or bending loads. U.S. Pat. No. 2,855,179 to Brown entitled "High Temperature Ceramic Turbine" is illustrative of one technique for holding ceramic rotor blades in compression. It is readily apparent, however, that centrifugal force techniques for applying compressive loads to the ceramic blades in Brown are inapplicable to stationary structure such as the stator vane assembly discussed herein.
Continuing efforts are underway to make the benefits of ceramic stator materials available for use within the turbine environment of a gas turbine engine.